There has been substantial research and commercial interest in enzyme immobilization technology. It has primarily focused upon simple, single enzyme systems; for example, ones which catalyze one-step degenerative or isomerization reactions. Immobilization has been accomplished by a number of means within the general categories of attachment of the enzyme to solid supports; entrapment within a porous gel; and various chemical linking techniques.
There has also been some interest in multi-enzyme systems. Commonly, this has involved immobilization of whole cell preparations. Immobilized cellular preparations have the additional advantage that they may contain co-factors native to the cells. These may accelerate desired single or multi-step reactions. Because whole cells are involved, however, use of these catalysts may be limited by complications arising from the native limits imposed by the cells themselves and by natural cellular metabolisms.
The use of immobilizing supports appears to have been practiced primarily to facilitate handling of enzymes during use. It is well known, for example, that immobilization permits treatment of greater amounts of substrate. It fixes the location of the enzyme within the reaction zone and readily allows separation of the treated substrate and/or product from enzyme after the reaction has occurred.
The fields of use of enzyme and immobilized enzyme systems in the prior art has been quite broad. For example, the isomerization of glucose with an enzyme present in immobilized, whole cell preparations is disclosed in Biotechnol. Bioeng., 15, 565 by Vieth et al. (1973). Other representative mention of such systems and specific facets thereof may be found in Immobilized Enzymes Preparation and Engineering Techniques, Gutcho, Noyes Data Corporation (1974) and Biotechnology and Bioengineering, Vol. XIX, pp. 387-397 by Kierstan et al. (1977).
While immobilized enzyme catalysts for carbohydrate (especially sugar and starch conversion) reactions have particularly high commerical interests, a variety of complications have heretofore limited their use. Whole cell catalysts, for example, often lead to low yield and interfering by-products. Conversely, the number of enzyme steps necessary for a given conversion may make their use uneconomic.
In addition, any use of enzymes as catalysts requires consideration of their operational life, and this is no less the case in carbohydrate conversion reactions. A serious problem encountered in the use of enzymes (in immobilized or free form) involves their inactivation by constituents native to the enzyme source or produced during their isolation and/or use. Thus, there are numerous reports respecting inactivating agents and means for overcoming their effects. These include Baijal et al., Phytochem. 11:929 (1972); Hawker, Phytochem. 8:9 (1969); Palmer et al., Aust. J. Biol. Sci. 22:87 (1969); Burg et al., Plant Physiol. 39:185 (1964); and Sacher, Nature 195:577 (1962)--describing the adverse effects of phenolic content of many vegetable materials on enzyme activity--and Loomis et al., Phytochem. 5:423 (1966); Anderson, Phytochem. 7:1973 (1968); and Loomis, Methods in Enzymol. 31:258 (1974)--describing means for reducing enzyme inactivation resultant from the different browning reactions in vegetable materials.
In all fields of use, however, substantial impediments remain. Moreover, commercialization of enzyme catalysts in many has heretofore been wholly uneconomic because of these drawbacks.